With increasingly strict regulation of engine emissions, the use of exhaust treatment devices has increased over the past several years. These devices include filters (e.g., diesel particulate filters or DPF) to trap particulate matter and devices to trap or convert nitrogen oxides (NOx) to less harmful gases. As is known, DPF devices must be regenerated to avoid excessive accumulation of particulate matter in the device. To avoid removing the DPF for cleaning, it is convenient to regenerate the DPF in place by burning or oxidizing the particulate matter. When the engine is operated at high load, the temperature of the exhaust gas exiting the engine may be sufficiently high to cause burning of the particulate matter in the DPF, particularly if the DPF includes a catalytic coating for converting NO in the exhaust stream to NO2 to facilitate NO2 based regeneration of the particulate matter.
The following publications are representative of existing technology and are incorporated herein by reference for the content of their disclosures.
U.S. Pat. No. 4,902,487 to Cooper et al. discloses an exhaust treatment arrangement including a catalyst to convert NO to NO2 upstream of a particulate filter to trap particulate matter. The NO2 reacts with the trapped particulate matter to oxidize it and keep the filter relatively clean of trapped matter.
U.S. Pat. No. 5,746,989 to Murachi et al. discloses an apparatus including a catalyst to convert NO to NO2, a diesel particulate filter to trap particulate matter, the NO2 being introduced to the particulate filter to oxidize trapped particulate matter, and an NO trap downstream of the particulate filter to absorb NOx from the gas stream.
U.S. Pat. No. 6,662,553 to Patchett et al. discloses a system for the selective catalytic reduction (SCR) of NOx in an exhaust gas stream by the use of urea as a reductant. The document includes a discussion of various known methods of reducing NOx in gas streams.
U.S. Pat. No. 6,805,849 to Andreasson et al. discloses an apparatus for removing NOx and particulate matter from an exhaust gas stream including an oxidizing catalyst for converting NO to NO2, a particulate filter downstream of the oxidizing catalyst, whereby the NO2 thus provided to the particulate filter oxidizes the particulate matter to remove it from the filter, and an SCR device downstream of the particulate filter to convert NOx exiting the particulate filter to water and N2 by reaction with ammonia in the presence of a catalyst.
United States Patent Application Publication No. 2006/0196176 by Karlsson et al., which is owned in common with the present application, discloses an apparatus for adjusting the temperature of exhaust gas from an engine, including an oxidation catalyst connected to receive exhaust gas from an engine, diesel particulate filter downstream of the oxidation catalyst, and a heat exchanger connected upstream of the oxidation catalyst in the exhaust flow and connected to receive the flow exiting the diesel particulate filter. The heated flow from the regeneration of particulate in the diesel particulate filter loops back to heat the engine exhaust flow before it enters the oxidation catalyst.
The invention provides an apparatus for treating engine exhaust gas, comprising an exhaust conduit for leading exhaust gases from an engine to an outlet, a particulate filter connected in the exhaust conduit to receive exhaust gas, a heat source connected in the exhaust conduit upstream of the particulate filter, and a heat exchanger connected to receive exhaust gas exiting the particulate filter and arranged to heat a portion of the exhaust conduit upstream of the heat source and particulate filter.
According to one embodiment, the heat exchanger comprises a pipe surrounding the particulate filter, the heat source, and the portion of the exhaust conduit upstream of the heat source and particulate filter, the pipe receiving exhaust gas exiting the particulate filter and guiding the exhaust gas to flow in heat exchanging contact with the particulate filter, the heat source, and the portion of the exhaust conduit.
The exhaust conduit includes a further portion downstream of the pipe to guide exhaust gas exiting the pipe to the outlet.
According to an alternative embodiment, the heat exchanger comprises a housing having a first inlet to receive exhaust gas from the engine and a first outlet connected upstream of the heat source, and having second inlet to receive exhaust gas exiting the particulate filter and a second outlet connected to the exhaust conduit, the heat exchanger configured to put the exhaust gas entering the second inlet in heat transfer contact with gas entering the first conduit.
According to an aspect of the alternative embodiment a heat insulating jacket surrounds the heat source and particulate filter.
According to yet another aspect, a bypass conduit is connected in the exhaust conduit upstream of the first inlet of the heat exchanger and downstream of the first outlet of the heat exchanger, the bypass conduit having a valve controlled for selectively directing exhaust gas into the heat exchanger or to avoid the heat exchanger.
According to another aspect of the invention, the apparatus further comprises a catalytic device for reducing nitrogen oxides connected in the conduit downstream of the heat exchanger. An injector may be mounted to the conduit upstream of the catalytic device for injecting a reductant into the exhaust gas. The catalytic device may be a selective catalytic reduction apparatus.
According to yet another aspect of the invention, the apparatus further comprises a slip catalyst device connected in the conduit downstream of the catalytic device for reducing nitrogen oxides.
An ammonia sensor may be mounted in the conduit downstream of the slip catalyst device and used to control the slip catalyst.
According to the invention, the heat source may be a diesel oxidation catalyst device, a burner device connectable to a fuel source, or an electrical heating device.
The particulate filter may include a catalytic coating for converting NO to NO2. Alternatively, or in addition, a heat source configured as a diesel oxidation catalyst may include a catalytic coating for converting NO to NO2. As yet another alternative, a single device may be provided combining the particulate filter, catalytic coating for converting NO to NO2, and the diesel oxidation catalyst functions.